This invention pertains in general to microsurgery of tissue, and more specifically to procedures and devices for accessing a tissue through another tissue layer, to cut or otherwise manipulate that tissue. For example, the procedures and devices can be used to deliver an ophthalmic surgical device through the cornea to the anterior lens capsule membrane in the anterior chamber of an eye.
Lens cataract is the leading cause of blindness worldwide and surgical treatment by cataract removal is the treatment of choice. A cataract is a clouding that develops in the lens of the eye or in its envelope. The creation of areas of opacity in the lens obstructs the passage of light. The lens of the eye is supposed to be transparent. If the lens develops opaque areas, as in a cataract, the lens must be surgically removed. If no lens is present in the eye, corrective glasses are required to focus an image on the retina. The lens, however, can be replaced with an artificial intraocular lens (IOL) to provide better vision after cataract removal. There may also be other reasons such as presbyopia to replace a lens that is not serving its functions appropriately.
The removal of the lens for replacement with an IOL is a surgical procedure that requires substantial precision. The lens is completely enclosed by a membrane called the lens capsule, so the surgeon must first cut through the capsule to access the lens. It is important to cut the capsule in just the right way. If the lens capsule has been cut correctly, and not damaged during the cataract removal, then it can be used to hold an IOL. The implantation of an IOL requires the creation of an opening in the lens capsule that is precisely centered, sized, and shaped for implant stability and for optimal IOL function. The matching of the lens capsule opening size to the peripheral margins of the IOL is critical. The goal of the surgeon is to create a perfectly circular (e.g., 5.5+/−0.1 mm diameter) hole in the capsular membrane (i.e., the lens capsule) that encapsulates the lens, centered on the optical axis of the eye, with no tears or defects in the edge of the hole. Tears or defects on the edge of the hole make the capsule very weak and vulnerable to losing the ability to hold the IOL properly. Different IOL designs may require a different diameter for the hole (e.g., ranging from 4.5+/−0.1 mm to 6.0+/−0.1 mm), but whatever the prescribed diameter is, the accuracy of the surgeon in actually achieving it is very important for proper outcome of the cataract surgery. This is especially true of IOLs intended to perform complex optical and focusing functions.
Creating an opening in the lens capsule with this required level of precision is a difficult task for a surgeon controlling and guiding conventional handheld cutting instruments and attempting to trace a precise circular route on the lens capsule. Currently, to perform a capsulotomy (the creation of an opening in the lens capsule), the surgeon typically manually creates a small tear in the anterior region of the lens capsule. With great caution, the surgeon then uses a small forceps to try to extend the edge of the tear so as to follow a circular path of the specified diameter and centered on the optic axis of the eye. In practice, it often happens that the hole does not end up circular, or the correct diameter, or centered on the optic axis. There can also be radial tears in the edge of the hole that greatly weaken the capsule. As a result of any of these errors, the capsule may not be able to hold the IOL properly, and optimal visual outcome cannot be achieved.
In addition to the difficulties faced by the surgeon in accessing the lens by performing a precise capsulotomy of the lens capsule, the surgeon must also be able to access the lens capsule itself. The lens is positioned in the anterior chamber of the eye. To access the lens capsule, the surgeon must create an incision in the cornea and carefully insert the capsulotomy instruments through this incision. The same requirement exists in a number of microsurgery procedures in which an incision in a first layer of tissue must be passed through before a second layer of tissue, behind or beneath that first layer, can be accessed. For the surgeon to maneuver the microsurgery instruments through the corneal incision, the incision must be of sufficient size to accommodate these instruments. However, the larger the incision, the greater the risk of infection, of corneal distortion, astigmatism, and of other complications. Microsurgery instruments commonly are not compact enough or are not sufficiently streamlined in shape, making it difficult for the surgeon to minimize the incision size or possibly risking tears or other damage at the incision site. Cutting elements or other sharp components are sometimes exposed during insertion, requiring the surgeon to be very precise and creating further risk of collateral damage to tissue when inserting the instrument through the incision. Further, this insertion often requires multiple steps and sometimes complex maneuvering of instruments by the surgeon, leaving little room for error. Once inserted, instruments are often not easily manipulated and the surgeon may be forced to handle and move multiple separate pieces in a small space. Any of these problems can make it very difficult for a surgeon to access a second layer of tissue behind a first layer, particularly when the second layer is tissue in a very small area, such as within the eye.
Given the drawbacks of existing treatment devices/procedures for accessing tissue, such as the lens capsule, to perform surgery, improved techniques and devices for performing microsurgery are needed.